Fuel systems for gas turbine engines



March'S, 1968 E. H. WARNE 3,371,481

FUEL SYSTEMS FOR GAS TURBINE ENGINES Filed NOV. 8, 1966 United States Patent tiice 3,371,481 FUEL SYSTEMS FOR GAS TURBINE ENGINES Eugene Harold Warne, Shirley, Solihull, England, assignor to Joseph Lucas (Industries) Limited, Birmingham, England Filed Nov. 8, 1966, Ser. No. 592,901 4 Claims. (Cl. Gil-39.28)

This invention relates to fuel systems for gas turbine engines, and of the kind having a throttle controllable manually, and also controllable in accordance with changes in a pressure which varies with that in the engine air intake.

The object of this invention is to provide an acceleration control for use with a fuel system as referred to.

In accordance with a primary aspect of the present invention an acceleration control for a gas turbine engine fuel system comprises a throttle, a manual control for the throttle, a further device also for controlling the throttle, said further device being responsive to changes in pressure conditions within the engine with which the system is associated, a cam connected to the throttle so as to be movable therewith, a spring acting between the cam and a valve member, means responsive to changes in the speed of the engine and acting upon the valve member in opposition to the spring, the valve member being arranged to modify the response of said pressure upon the further device for controlling the throttle, the arrangement being such that manual opening of the throttle will increase the load exerted by the spring to actuate the valve to modify the further device in a manner to tend to close the throttle, the resultant force upon the throttle causing its opening rate to be controlled until the engine speed increases to an extent to again actuate the valve member, whereupon equilibrium conditions will be obtained to maintain the engine speed at a new value.

In accordance with a further aspect the invention resides in the provision of a fuel system comprising a pump having a delivery passage to burners in an associated engine, and a throttle `and acceleration control as set forth in the preceding paragraph.

The invention will now be described by way of example with reference to the accompanying drawing which is a diagrammatic representation of a 4fuel system for a gas turbine engine.

The fuel system includes an engine driven pump of the swash-plate type arranged to obtain a supply of fuel from a reservoir (not shown) through an inlet passage 11 and connected to a passage 12 leading to burners (not shown) in the engine. The passage 12 passes through a body 13 containing a throttle 14 in the passage 12, the throttle being in the form of a hollow plunger having a tapered end and movable lengthwise with respect to an annular seating 15. Also within the body 13 and associated with the throttle 14 is a device for maintaining constant pressure drop across the throttle. 'Ihis device is a valve 16 controlling escape of fuel from a servo mechanism 17 associated with the pump for controlling its stroke, t-he opening of the valve 16 being determined by the pressures existing at the upstream and downstream sides of the throttle 14 acting upon a piston 18 which in turn exerts la force on the valve 16.

'Ihe throttle 14 is movable through a Ipinion 19 on a shaft 20 by a linkage which can either be actuated by a manual lever 21 or in response to changes in air pressure conditions in the engine, in a manner to be described. The linkage which is connected in the shaft 20 through an arm 22 and a universally jointed rod 23 has a two armed lever 24 mounted on a shaft 25, one of the arms of the lever 24 carrying a bell crank 26, one limb of Which is connected through a universally jointed rod 27 and lost motion pin and slot connection 28, to the manual 3,371,481 Patented Mar. 5, 1968' lever 21, and the other limb of the bell crank 26 is connected to the rod 23 to the throttle 14. The other arm of the lever 24 is connected, through a further universally jointed rod 29 to a member 30 which is controlled in a manner to be described.

The linkage is preferably however so constructed that it is capable of occupying a position in which the manual lever 21 can be moved without moving the throttle 14, or a further position in which movement of the member 30 has no effect upon the throttle.

The member 30 moves in response to changes in t-he ratio of two pressures exerted respectively in the passages 31, 32. In this example the pressures are atmospheric pressure and that obtaining in the engine intake respectively. The passages 31, 32 have respective restrictors 33, 34 and the intermediate pressure is exerted upon an evacuated bellows 35 mounted in a chamber 36 in the Abody 13. The bellows 35 is -connected to a valve member 37 controlling the pressure in a cylinder 38 containing a piston 39 to which the member 30 is connected. Pressure conditions in the cylinder 38 are derived from the pump outlet passage 12, at a position upstream of the throttle 14, one end of the cylinder being supplied therefrom through a restrictor 40. Escape of fuel takes place past the valve 37 through a passage 41 communicating through a further passage 42 with the pump inlet passage 11. A spring 43 acts between the piston 39 and the valve member 37.

The arrangement of this portion of the apparatus is such that a signal which varies with the engine air intake pressure is applied through the valve member 37 and thence through the spring 43 to the piston 39. Movement of the valve member 37 opens the cylinder 38 to the passage 41. This causes movement of the piston 39 to compress the spring 43 so that it exerts a pressure to close the valve. Movement of the piston 39 causes the linkage to take up a new position which in turn alters the setting of the throttle 14. As described, such movement of the piston 39 causes a feed back which arrests the piston in its new position.

When accelerating a gas turbine engine, it is necessary to supply an additional quantity of fuel, and to provide for this, the system shown in the drawing includes a cam 44 which is attached to the lever spindle 20 carrying the throttle operating pinion 19, this cam 44 bearing against an abutment plate 45 for a compression spring 46, the opposite end of which bears upon a further abutment plate 47 carried by a valve member 4S. The valve member 48 is arranged to control iiow of fuel through a passage 49 which communicates with the end of the cylinder 38 remote from the spring 43. The valve member 48 is pivotally mounted on a fixed support in the body 13 in its mid-region indicated by numeral 49 and acting against the spring 46 is a bellows 50 which is evacuated and which is disposed in a chamber 51 to the interior of which is supplied, in use, a pressure which is responsive to engine speed, and which is substantially higher than the pressure on the bellows35. This pressure is an intermediate pressure corresponding to the ratio of the pressure, exerted in two passages 52, 53 having restrictors 54, 55 respectively. The pressure in the passage 52 is the pressure at the upstream side of the engine compressor and that in the passage 53 is the pressure at the downstream side of the compressor, or of a first compressor thereof as the case may be.

ln use under steady running conditions, the valve member 48 provides limited ow from the cylinder 38 and the position of the linkage is determined by a setting ofthe manual lever 21 and also by the pressure on the bellows 35, the latter determining the position of the valve member 37 and thus the position of the piston 39 3 in the cylinder 38, as modied by the flow past the valve member 48.

If it is desired to accelerate the engine, the manual lever 21 is moved to a new setting, thus moving the throttle 14 to the right as seen in the drawing. The cam 44 is also moved and this increases the preload of the spring 46, thus overcoming the force resulting from the pressure on the bellows 50 and closing the valve and preventing escape of fuel from the end of the cylinder 38 to the pump inlet 11, through the body 13, thus creating a build up of pressure to cause the piston to move in a direction to move the linkage to tend to close the throttle 14. The resultant force upon the throttle tends to move it relatively slowly and provides an additional quantity of fuel for acceleration purposes. The increasing speed of the engine causes the value of the pressure in the passage 53 to rise, this causing the bellows 50 to collapse thus creating a force for reopening the valve to permit escape of fuel from the cylinder 38 past the valve member 48 and through the body 13 to the pump inlet passage 11. This then permits the piston 39 to return to a position in which equilibrium conditions are obtained, the throttle 14 arriving at a position to maintain the required fuel flow to the engine to run it at the desired new higher speed.

It will be apparent that under deceleration conditions, there will be no tendency for the valve member 48 to move to close the valve since the pressure on the bellows 50 will always, during deceleration, provide a force less than the rating of the spring 46.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. An acceleration control for a gas turbine engine fuel system comprising a throttle, a manual control for the throttle, a further device also for controlling the throttle, said further device being responsive to changes in pressure conditions within the engine with which the system is associated, a cam connected to the throttle so as to be movable therewith, a spring acting between the cam and a valve member, means responsive to changes in the speed of the engine and acting upon the Valve member in opposition to the spring, the valve member being arranged to modify the response of said pressure conditions upon the further device for controlling the throttle.

2. An acceleration control as claimed in claim 1 in which the further device is a piston and cylinder device, passage means being provided for supplying fuel under pressure thereto, and said pressure conditions in the engine controlling a further valve member arranged to control the escape of Vfuel from one end of the cylinder, the first mentioned valve member also controlling escape of fuel from the same end of the cylinder of the device.

3. A fuel system for a gas turbine engine comprising a pump having a delivery passage, to burners in an associated engine, and an acceleration control comprising a throttle in said delivery passage, a manual control for the throttle, a further device also for controlling the throttle, said further device being responsive to changes in pressure conditions within the engine with which the system is associated, a cam connected to the throttle so as to be movable therewith, a spring acting between the cam and a valve member, means responsive to changes in the speed of the engine and acting upon the valve member in opposition to the spring, the valve member being arranged to modify the response of said pressure conditions upon the further device for controlling the throttle.

4. A fuel system as claimed in claim 3 in which there is a device for maintaining substantially constant pressure drop across the throttle, said device being arranged to control the output of the pump through an associated servo mechanism.

References Cited UNITED STATES PATENTS JULIUS E. WEST, Primary Examiner. 

1. AN ACCELERATION CONTROL FOR A GAS TURBINE ENGINE FUEL SYSTEM COMPRISING A THROTTLE, A MANUAL CONTROL FOR THE THROTTLE, A FURTHER DEVICE ALSO FOR CONTROLLING THE THROTTLE, SAID FURTHER DEVICE BEING RESPONSIVE TO CHANGES IN PRESSURE CONDITIONS WITHIN THE ENGING WITH WHICH THE SYSTEM IS ASSOCIATED, A CAM CONNECTED TO THE THROTTLE SO AS TO BE MOVABLE THEREWITH, A SPRING ACTING BETWEEN THE CAM AND A VALVE MEMBER, MEANS RESPONSIVE TO CHANGES IN THE SPEED OF THE ENGINE AND ACTING UPON THE VALVE MEMBER IN OPPOSITION TO THE SPRING, THE VALVE MEMBER BEING ARRANGED TO MODIFY THE RESPONSE TO SAID PRESSURE CONDITIONS UPON THE FURTHER DEVICE FOR CONTROLLING THE THROTTLE. 